Details of a Researcher - Hanaoka, Kenjiro

Papers - Hanaoka, Kenjiro

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Red fluorescent scaffold for highly sensitive protease activity probes

Kushida Y., Hanaoka K., Komatsu T., Terai T., Ueno T., Yoshida K., Uchiyama M., Nagano T.

Bioorganic and Medicinal Chemistry Letters (Bioorganic and Medicinal Chemistry Letters) 22 ( 12 ) 3908 - 3911 2012.06

Research paper (scientific journal), Accepted, ISSN 0960894X

We have developed a novel red fluorescent dye, 2Me SiR600 (λem = 613 nm), in which the O atom of Rhodamine Green at the 10 position of the xanthene moiety is replaced with a Si atom, as a scaffold for probes to detect protease activity with extremely high S/N ratio. As proof of concept, we designed and synthesized probes for caspase-3 activity (Z-DEVD-SiR600) and leucine aminopeptidase activity (Leu-SiR600). Caspase-3-mediated cleavage of Z-DEVD-SiR600 resulted in a large bathochromic shift (93 nm) of the absorption maximum and a 432-fold fluorescence enhancement. © 2012 Elsevier Ltd. All rights reserved.

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Near-infrared fluorescence probes for enzymes based on binding affinity modulation of squarylium dye scaffold

Oushiki D., Kojima H., Takahashi Y., Komatsu T., Terai T., Hanaoka K., Nishikawa M., Takakura Y., Nagano T.

Analytical Chemistry (Analytical Chemistry) 84 ( 10 ) 4404 - 4410 2012.05

Research paper (scientific journal), Accepted, ISSN 00032700

We present a novel design strategy for near-infrared (NIR) fluorescence probes utilizing dye-protein interaction as a trigger for fluorescence enhancement. The design principle involves modification of a polymethine dye with cleavable functional groups that reduce the dye's protein-binding affinity. When these functional groups are removed by specific interaction with the target enzymes, the dye's protein affinity is restored, protein binding occurs, and the dye's fluorescence is strongly enhanced. To validate this strategy, we first designed and synthesized an alkaline phosphatase (ALP) sensor by introducing phosphate into the squarylium dye scaffold; this sensor was able to detect ALP-labeled secondary antibodies in Western blotting analysis. Second, we synthesized a probe for β-galactosidase (widely used as a reporter of gene expression) by means of β-galactosyl substitution of the squarylium scaffold; this sensor was able to visualize β-galactosidase activity both in vitro and in vivo. Our strategy should be applicable to obtain NIR fluorescence probes for a wide range of target enzymes. © 2012 American Chemical Society.

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Development of hypoxia-sensitive Gd <sup>3+</sup>-based MRI contrast agents

Iwaki S., Hanaoka K., Piao W., Komatsu T., Ueno T., Terai T., Nagano T.

Bioorganic and Medicinal Chemistry Letters (Bioorganic and Medicinal Chemistry Letters) 22 ( 8 ) 2798 - 2802 2012.04

Research paper (scientific journal), Accepted, ISSN 0960894X

Hypoxia occurs in various diseases, including cancer, ischemia, and acute and chronic vascular diseases. Here we describe the design and synthesis of the first hypoxia-sensitive MRI contrast agents, SAGds. SAGds showed a pH-dependent r 1 relaxivity change associated with intramolecular chelation of the nitrogen atom of the sulfonamide moiety to the Gd 3+ center. There was a correlation between the pK a of the r 1 relaxivity change and the sum of the Hammett σ constants of substituents on the aromatic ring. Among the synthesized compounds, 4NO 22MeOSAGd was selectively reduced to the amine by rat liver microsomes under hypoxic conditions, resulting in a 1.8-fold increment of the r 1 relaxivity owing to the change in pK a of the arylsulfonamide moiety. This enhancement of the r 1 relaxivity could be clearly detected in T 1-weighted MR images. Thus, 4NO 22MeOSAGd is a 'smart' MRI contrast agent for the detection of hypoxia under physiological conditions. © 2012 Elsevier Ltd. All rights reserved.

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Development of NIR fluorescent dyes based on Si-rhodamine for in vivo imaging

Koide Y., Urano Y., Hanaoka K., Piao W., Kusakabe M., Saito N., Terai T., Okabe T., Nagano T.

Journal of the American Chemical Society (Journal of the American Chemical Society) 134 ( 11 ) 5029 - 5031 2012.03

Research paper (scientific journal), ISSN 00027863

We have developed a series of novel near-infrared (NIR) wavelength-excitable fluorescent dyes, SiR-NIRs, by modifying the Si-rhodamine scaffold to obtain emission in the range suitable for in vivo imaging. Among them, SiR680 and SiR700 showed sufficiently high quantum efficiency in aqueous media. Both antibody-bound and free dye exhibited high tolerance to photobleaching in aqueous solution. Subcutaneous xenograft tumors were successfully visualized in a mouse tumor model using SiR700-labeled anti-tenascin-C (TN-C) antibody, SiR700-RCB1. SiR-NIRs are expected to be useful as labeling agents for in vivo imaging studies including multicolor imaging, and also as scaffolds for NIR fluorescence probes. © 2012 American Chemical Society.

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A reversible near-infrared fluorescence probe for reactive oxygen species based on Te-rhodamine

Koide Y., Kawaguchi M., Urano Y., Hanaoka K., Komatsu T., Abo M., Terai T., Nagano T.

Chemical Communications (Chemical Communications) 48 ( 25 ) 3091 - 3093 2012.02

Research paper (scientific journal), Accepted, ISSN 13597345

We have designed and synthesized a reversible near-infrared (NIR) fluorescence probe, 2-Me TeR, for reactive oxygen species (ROS), utilizing the redox properties of the tellurium (Te) atom. 2-Me TeR is oxidized to fluorescent 2-Me TeOR by various ROS, while the generated 2-Me TeOR is quickly reduced in the presence of glutathione to regenerate 2-Me TeR. This redox-induced reversible NIR-fluorescence response of 2-Me TeR allowed us to detect the endogenous production of ROS and subsequent homeostatic recovery of the intracellular reductive environment in hydrogen peroxide-stimulated HL-60 cells. This probe is expected to be useful for monitoring the dynamics of ROS production continuously in vivo © 2012 Royal Society of Chemistry.

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Selective two-step labeling of proteins with an off/on fluorescent probe

Hirabayashi K., Hanaoka K., Shimonishi M., Terai T., Komatsu T., Ueno T., Nagano T.

Chemistry - A European Journal (Chemistry - A European Journal) 17 ( 52 ) 14763 - 14771 2011.12

Research paper (scientific journal), Accepted, ISSN 09476539

We present a novel design strategy for off/on fluorescent probes suitable for selective two-step labeling of proteins. To validate this strategy, we designed and synthesized an off/on fluorescent probe, 1-Ni 2+, which targets a cysteine-modified hexahistidine (His) tag. The probe consists of dichlorofluorescein conjugated with nitrilotriacetic acid (NTA)-Ni 2+ as the His-tag recognition site and a 2,4-dinitrophenyl ether moiety, which quenches the probe's fluorescence by photoinduced electron transfer (PeT) from the excited fluorophore to the 2,4-dinitrophenyl ether (donor-excited PeT; d-PeT) and also has reactivity with cysteine. His-tag recognition by the NTA-Ni 2+ moiety is followed by removal of the 2,4-dinitrophenyl ether quencher by proximity-enhanced reaction with the cysteine residue of the modified tag; this results in a marked fluorescence increase. Addition of His-tag peptide bearing a cysteine residue to aqueous probe solution resulted in about 20-fold fluorescence increment within 10 min, which is the largest fluorescence enhancement so far obtained with a visible light-excitable fluorescent probe for a His-based peptide tag. Further, we successfully visualized CysHis 6-peptide tethered to microbeads without any washing step. The probe also showed a large fluorescence increment in the presence of His 6Cys-tagged enhanced blue fluorescent protein (EBFP), but not His 6-tagged EBFP. We consider this system is superior to large fluorescence tags (e.g., green fluorescent protein: 27 kDa), which can perturb protein folding, trafficking and function, and also to existing small tags, which generally show little fluorescence increase upon target recognition and therefore require a washout step. This strategy should also be applicable to other tags. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Development of a highly selective fluorescence probe for hydrogen sulfide

Sasakura K., Hanaoka K., Shibuya N., Mikami Y., Kimura Y., Komatsu T., Ueno T., Terai T., Kimura H., Nagano T.

Journal of the American Chemical Society (Journal of the American Chemical Society) 133 ( 45 ) 18003 - 18005 2011.11

Research paper (scientific journal), Accepted, ISSN 00027863

Hydrogen sulfide (H 2S) has recently been identified as a biological response modifier. Here, we report the design and synthesis of a novel fluorescence probe for H 2S, HSip-1, utilizing azamacrocyclic copper(II) ion complex chemistry to control the fluorescence. HSip-1 showed high selectivity and high sensitivity for H 2S, and its potential for biological applications was confirmed by employing it for fluorescence imaging of H 2S in live cells. © 2011 American Chemical Society.

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Method for enhancing cell penetration of Gd <sup>3+</sup>-based MRI contrast agents by conjugation with hydrophobic fluorescent dyes

Yamane T., Hanaoka K., Muramatsu Y., Tamura K., Adachi Y., Miyashita Y., Hirata Y., Nagano T.

Bioconjugate Chemistry (Bioconjugate Chemistry) 22 ( 11 ) 2227 - 2236 2011.11

Research paper (scientific journal), Accepted, ISSN 10431802

Gadolinium ion (Gd 3+) complexes are commonly used as magnetic resonance imaging (MRI) contrast agents to enhance signals in T 1-weighted MR images. Recently, several methods to achieve cell-permeation of Gd 3+ complexes have been reported, but more general and efficient methodology is needed. In this report, we describe a novel method to achieve cell permeation of Gd 3+ complexes by using hydrophobic fluorescent dyes as a cell-permeability-enhancing unit. We synthesized Gd 3+ complexes conjugated with boron dipyrromethene (BDP-Gd) and Cy7 dye (Cy7-Gd), and showed that these conjugates can be introduced efficiently into cells. To examine the relationship between cell permeability and dye structure, we further synthesized a series of Cy7-Gd derivatives. On the basis of MR imaging, flow cytometry, and ICP-MS analysis of cells loaded with Cy7-Gd derivatives, highly hydrophobic and nonanionic dyes were effective for enhancing cell permeation of Gd 3+ complexes. Furthermore, the behavior of these Cy7-Gd derivatives was examined in mice. Thus, conjugation of hydrophobic fluorescent dyes appears to be an effective approach to improve the cell permeability of Gd 3+ complexes, and should be applicable for further development of Gd 3+-based MRI contrast agents. © 2011 American Chemical Society.

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Development of a potassium ion-selective fluorescent sensor based on 3-styrylated BODIPY

Hirata T., Terai T., Komatsu T., Hanaoka K., Nagano T.

Bioorganic and Medicinal Chemistry Letters (Bioorganic and Medicinal Chemistry Letters) 21 ( 20 ) 6090 - 6093 2011.10

Research paper (scientific journal), Accepted, ISSN 0960894X

We have developed a red-emitting fluorescent K + probe, B3TAC, which also shows a wavelength shift upon binding to K +. The probe was synthesized by conjugating a cryptand-based chelator, 2-triazacryptand [2,2,3-1-(2-methoxyethoxy)benzene (TAC), to position 3 of the BODIPY fluorophore through a styryl linker. In water-acetonitrile mixed solvent, it responded to K + in the physiological concentration range with high selectivity over Na + and other metal ions. B3TAC is potentially useful for measuring cellular K + ion concentration, as well as for simple, naked-eye detection of K + in solution. © 2011 Elsevier Ltd. All rights reserved.

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Rational design of boron dipyrromethene (BODIPY)-based photobleaching- resistant fluorophores applicable to a protein dynamics study

Komatsu T., Oushiki D., Takeda A., Miyamura M., Ueno T., Terai T., Hanaoka K., Urano Y., Mineno T., Nagano T.

Chemical Communications (Chemical Communications) 47 ( 36 ) 10055 - 10057 2011.09

Research paper (scientific journal), Accepted, ISSN 13597345

We studied the photobleaching of a library of boron dipyrromethene (BODIPY) derivatives with a range of electron densities, and found that the photobleaching rate is influenced by the electron-withdrawing capacity of the substituents. Electron-deficient BODIPYs generated less singlet oxygen, were less reactive to singlet oxygen, and were highly resistant to photobleaching. We confirmed the utility of one of these fluorophores, 2,6-diCO2R-BDP, for visualizing EGF receptor dynamics in cells expressing an SNAP-tagged EGF receptor. © The Royal Society of Chemistry 2011.

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Development of a far-red to near-infrared fluorescence probe for calcium ion and its application to multicolor neuronal imaging

Egawa T., Hanaoka K., Koide Y., Ujita S., Takahashi N., Ikegaya Y., Matsuki N., Terai T., Ueno T., Komatsu T., Nagano T.

Journal of the American Chemical Society (Journal of the American Chemical Society) 133 ( 36 ) 14157 - 14159 2011.09

Research paper (scientific journal), Accepted, ISSN 00027863

To improve optical imaging of Ca 2+ and to make available a distinct color window for multicolor imaging, we designed and synthesized CaSiR-1, a far-red to near-infrared fluorescence probe for Ca 2+, using Si-rhodamine (SiR) as the fluorophore and the well-known Ca 2+ chelator BAPTA. This wavelength region is advantageous, affording higher tissue penetration, lower background autofluorescence, and lower phototoxicity in comparison with the UV to visible range. CaSiR-1 has a high fluorescence off/on ratio of over 1000. We demonstrate its usefulness for multicolor fluorescence imaging of action potentials (visualized as increases in intracellular Ca 2+) in brain slices loaded with sulforhodamine 101 (red color; specific for astrocytes) that were prepared from transgenic mice in which some neurons expressed green fluorescent protein. © 2011 American Chemical Society.

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Development of a highly selective fluorescence probe for alkaline phosphatase

Kawaguchi M., Hanaoka K., Komatsu T., Terai T., Nagano T.

Bioorganic and Medicinal Chemistry Letters (Bioorganic and Medicinal Chemistry Letters) 21 ( 17 ) 5088 - 5091 2011.09

Research paper (scientific journal), Accepted, ISSN 0960894X

We have developed the first highly selective fluorescence probe for alkaline phosphatase (ALP), TG-mPhos. This probe shows selectivity for ALP over protein tyrosine phosphatase and protein serine/threonine phosphatase. Our previously developed TG-Phos, which has a phenolic phosphate linkage in place of the alcoholic phosphate linkage of TG-mPhos, lacks this selectivity. TG-mPhos should enable precise fluorescence imaging of ALP activity in biological applications. © 2011 Elsevier Ltd. All rights reserved.

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Fluorescence probe for lysophospholipase C/NPP6 activity and a potent NPP6 inhibitor

Kawaguchi M., Okabe T., Okudaira S., Hanaoka K., Fujikawa Y., Terai T., Komatsu T., Kojima H., Aoki J., Nagano T.

Journal of the American Chemical Society (Journal of the American Chemical Society) 133 ( 31 ) 12021 - 12030 2011.08

Research paper (scientific journal), Accepted, ISSN 00027863

Nucleotide pyrophosphatases/phosphodiesterases (NPPs) are ubiquitous membrane-associated or secreted ectoenzymes that have a role in regulating extracellular nucleotide and phospholipid metabolism. Among the members of the NPP family, NPP1 and -3 act on nucleotides such as ATP, while NPP2, -6, and -7 act on phospholipids such as lysophosphatidylcholine and sphingomyelin. NPP6, a recently characterized NPP family member, is a choline-specific glycerophosphodiester phosphodiesterase, but its functions remain to be analyzed, partly due to the lack of highly sensitive activity assay systems and practical inhibitors. Here we report synthesis of novel NPP6 fluorescence probes, TG-mPC and its analogues TG-mPC 3C, TG-mPC 5C, TG-mPENE, TG-mPEA, TG-mPhos, TG-mPA, TG-mPMe, and TG-mPPr. Among the seven NPPs, only NPP6 hydrolyzed TG-mPC, TG-mPC 3C, and TG-mPENE. TG-mPC was hydrolyzed in the cell lysate from NPP6-transfected cells, but not control cells, showing that it is suitable for use in cell-based NPP6 assays. We also examined the usefulness of TG-mPC as a fluorescence imaging probe. We further applied TG-mPC to carry out high-throughput NPP6 inhibitor screening and found several NPP6-selective inhibitors in a library of about 80 000 compounds. Through structure-activity relationship (SAR) analysis, we identified a potent and selective NPP6 inhibitor with an IC 50 value of 0.21 μM. Our NPP6-selective fluorescence probe, TG-mPC, and the inhibitor are expected to be useful to elucidate the biological function of NPP6. © 2011 American Chemical Society.

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Development of a highly sensitive fluorescence probe for hydrogen peroxide

Abo M., Urano Y., Hanaoka K., Terai T., Komatsu T., Nagano T.

Journal of the American Chemical Society (Journal of the American Chemical Society) 133 ( 27 ) 10629 - 10637 2011.07

Research paper (scientific journal), Accepted, ISSN 00027863

Hydrogen peroxide is believed to play a role in cellular signal transduction by reversible oxidation of proteins. Here, we report the design and synthesis of a novel fluorescence probe for hydrogen peroxide, utilizing a photoinduced electron transfer strategy based on benzil chemistry to control the fluorescence. The practical value of this highly sensitive and selective fluorescence probe, NBzF, was confirmed by its application to imaging of hydrogen peroxide generation in live RAW 264.7 macrophages. NBzF was also employed for live cell imaging of hydrogen peroxide generated as a signaling molecule in A431 human epidermoid carcinoma cells. © 2011 American Chemical Society.

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Aminoluciferins as functional bioluminogenic substrates of firefly luciferase

Takakura H., Kojima R., Urano Y., Terai T., Hanaoka K., Nagano T.

Chemistry - An Asian Journal (Chemistry - An Asian Journal) 6 ( 7 ) 1800 - 1810 2011.07

Research paper (scientific journal), Accepted, ISSN 18614728

Firefly luciferase is widely used as a reporter gene in assays to study gene expression, gene delivery, and so on because of its extremely high signal-to-noise ratio. The availability of a range of bioluminogenic substrates would greatly extend the applicability of the luciferin-luciferase system. Herein, we describe a design concept for functional bioluminogenic substrates based on the aminoluciferin (AL) scaffold, together with a convenient, high-yield method for synthesizing N-alkylated ALs. We confirmed the usefulness of ALs as bioluminogenic substrates by synthesizing three probes. The first was a conjugate of AL with glutamate, Glu-AL. When Glu-AL, the first membrane-impermeable bioluminogenic substrate of luciferases, was applied to cells transfected with luciferase, luminescence was not observed; that is, by using Glu-AL, we can distinguish between intracellular and extracellular events. The second was Cy5-AL, which consisted of Cy5, a near-infrared (NIR) cyanine fluorescent dye, and AL, and emitted NIR light. When Cy5-AL reacted with luciferase, luminescence derived from Cy5 was observed as a result of bioluminescence resonance energy transfer (BRET) from AL to Cy5. The NIR emission wavelength would allow a signal to be observed from deeper tissues in bioluminescence in vivo imaging. The third was biotin-DEVD-AL (DEVD=the amino acid sequence Asp-Glu-Val-Asp), which employed a caspase-3 substrate peptide as a switch to control the accessibility of the substrate to luciferase, and could detect the activity of caspase-3 in a time-dependent manner. This generalized design strategy should be applicable to other proteases. Our results indicate that the AL scaffold is appropriate for a range of functional luminophores and represents a useful alternative substrate to luciferin. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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Evolution of group 14 rhodamines as platforms for near-infrared fluorescence probes utilizing photoinduced electron transfer

Koide Y., Urano Y., Hanaoka K., Terai T., Nagano T.

ACS Chemical Biology (ACS Chemical Biology) 6 ( 6 ) 600 - 608 2011.06

Research paper (scientific journal), Accepted, ISSN 15548929

The absorption and emission wavelengths of group 14 pyronines and rhodamines, which contain silicon, germanium, or tin at the 10 position of the xanthene chromophore, showed large bathochromic shifts compared to the original rhodamines, owing to stabilization of the LUMO energy levels by σ *-π * conjugation between group 14 atom-C (methyl) σ * orbitals and a π * orbital of the fluorophore. These group 14 pyronines and rhodamines retain the advantages of the original rhodamines, including high quantum efficiency in aqueous media (φ fl = 0.3-0.45), tolerance to photobleaching, and high water solubility. Group 14 rhodamines have higher values of reduction potential than other NIR light-emitting original rhodamines, and therefore, we speculated their NIR fluorescence could be controlled through the photoinduced electron transfer (PeT) mechanism. Indeed, we found that the fluorescence quantum yield (φ fl) of Si-rhodamine (SiR) and Ge-rhodamine (GeR) could be made nearly equal to zero, and the threshold level for fluorescence on/off switching lies at around 1.3-1.5 V for the SiRs. This is about 0.1 V lower than in the case of TokyoGreens, in which the fluorophore is well established to be effective for PeT-based probes. That is to say, the fluorescence of SiR and GeR can be drastically activated by more than 100-fold through a PeT strategy. To confirm the validity of this strategy for developing NIR fluorescence probes, we employed this approach to design two kinds of novel fluorescence probes emitting in the far-red to NIR region, i.e., a series of pH-sensors for use in acidic environments and a Zn 2+ sensor. We synthesized these probes and confirmed that they work well. © 2011 American Chemical Society.

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Development of an Si-rhodamine-based far-red to near-infrared fluorescence probe selective for hypochlorous acid and its applications for biological imaging

Koide Y., Urano Y., Hanaoka K., Terai T., Nagano T.

Journal of the American Chemical Society (Journal of the American Chemical Society) 133 ( 15 ) 5680 - 5682 2011.04

Research paper (scientific journal), Accepted, ISSN 00027863

A far-red to near-infrared (NIR) fluorescence probe, MMSiR, based on Si-rhodamine, was designed and synthesized for sensitive and selective detection of HOCl in real time. MMSiR and its oxidized product SMSiR have excellent properties, including pH-independence of fluorescence, high resistance to autoxidation and photobleaching, and good tissue penetration of far-red to NIR fluorescence emission. The value of MMSiR was confirmed by real-time imaging of phagocytosis using a fluorescence microscope. wsMMSiR, a more hydrophilic derivative of MMSiR, permitted effective in vivo imaging of HOCl generation in a mouse peritonitis model. This probe is expected to be a useful tool for investigating the wide range of biological functions of HOCl. © 2011 American Chemical Society.

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Positive correlation between the generation of reactive oxygen species and activation/reactivation of transgene expression after hydrodynamic injections into mice

Takiguchi N., Takahashi Y., Nishikawa M., Matsui Y., Fukuhara Y., Oushiki D., Kiyose K., Hanaoka K., Nagano T., Takakura Y.

Pharmaceutical Research (Pharmaceutical Research) 28 ( 4 ) 702 - 711 2011.04

Research paper (scientific journal), Accepted, ISSN 07248741

Purpose: Hydrodynamic injection has been shown to reactivate silenced transgene expression in mouse liver. In this study, the roles of inflammatory cytokines and reactive oxygen species (ROS) in the reactivation were examined. Methods: Production of inflammatory cytokines and ROS by hydrodynamic injection of saline was examined in mice that had received a hydrodynamic injection of a plasmid expressing Gaussia luciferase. The level of reporter gene expression was used as an indicator of the reactivation. The involvement of cytokines and ROS was examined by depleting Kupffer cells or by pre-administration of antioxidants, respectively. Results: A hydrodynamic injection of saline induced a significant production of interleukin (IL)-6. Depleting Kupffer cells using clodronate liposomes markedly reduced the IL-6 production but had no significant effect on the transgene expression. On the other hand, an injection of catalase or N-acetylcysteine significantly inhibited the hydrodynamic injection-induced reactivation of silenced transgene expression. The silenced expression was also reactivated by carbon tetrachloride, an inducer of oxidative stress in the liver, in a dose-dependent manner, and this reactivation was significantly inhibited by catalase. Conclusions: These findings show a positive correlation between the generation of ROS and the reactivation of silenced transgene expression after hydrodynamic injections. © 2010 Springer Science+Business Media, LLC.

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Development of a fluorescein analogue, TokyoMagenta, as a novel scaffold for fluorescence probes in red region

Egawa T., Koide Y., Hanaoka K., Komatsu T., CooTeraiper T., Nagano T.

Chemical Communications (Chemical Communications) 47 ( 14 ) 4162 - 4164 2011.03

Research paper (scientific journal), Accepted, ISSN 13597345

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Rational design of ratiometric near-infrared fluorescent pH probes with various pK<inf>a</inf> values, based on aminocyanine

Myochin T., Kiyose K., Hanaoka K., Kojima H., Terai T., Nagano T.

Journal of the American Chemical Society (Journal of the American Chemical Society) 133 ( 10 ) 3401 - 3409 2011.03

Research paper (scientific journal), Accepted, ISSN 00027863

Novel ratiometric, near-infrared fluorescent pH probes with various pK a values have been designed and synthesized on the basis of aminocyanine bearing a diamine moiety, and their photochemical properties were evaluated. Under acidic conditions, these pH probes showed a 46- to 83-nm red shift of the absorption maximum. This change is sufficiently large to permit their use as ratiometric pH probes, and is reversible, whereas monoamine-substituted aminocyanines showed irreversible changes because of their instability under acidic conditions. Furthermore, the pKa values of these probes can be predicted from the calculated pKa values of the diamine moieties, obtained from the SciFinder database. This design strategy is very simple and flexible, and should be applicable to develop NIR pH probes for various applications. © 2011 American Chemical Society.

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